This invention relates to a load-bearing motor bus structure comprising a frame, a pair of body sides, a front panel, a rear panel and a roof.
In structures of this type, these elements are normally joined together by welding, and by the use of gusset plates of various types interposed between the parts to be joined together. Structures obtained in this manner have certain drawbacks.
Firstly, in addition to the actual welding, supplementary operations are required in order to prepare the parts to be joined together and to protect them from the action of external agents once joined. In this respect, the protection paint layer has to be removed from the surface of those parts to be joined together in order to give access to the metal surface on which the weld seams are to be applied, each connection node then having to be again painted when welding has been completed. In addition, corrosion can easily arise at each of these nodes because the protection obtained by the supplementary painting can be incomplete because of the difficulty of applying the protective paint over the entire surface of the node which is exposed to the action of external agents.
Again, in correspondence with each node, deformation of the joined parts can arise or alteration can occur in the material crystalline structure, with the result that mechanical strength is considerably reduced. The operations required to form such structures are carried out under rather uncomfortable conditions because of the presence of noise and gas, which also influences the quality of the joints obtained.
Furthermore, only parts constructed of the same weldable material can be joined together in the described manner, thus limiting the choice of the economically and operationally most correct design. The parts to be joined together cannot be fitted with installed units before undergoing joining, because of the damage which these units can undergo on account of the fairly high temperature required to make the joints, on account of the gas present, and on account of the foreign substances which come into contact with the inner surfaces of the structural parts. The joints made in the described manner do not allow the parts to be moved relative to each other for any final adjustment of the relative positions of the parts themselves, nor do they allow actual disassembly to be carried out. Because of the considerable dimensions of the structure, serious problems also arise in handling the welding heads. Finally, the production versatility in terms of modifying already prewelded structures is poor, and it is necessary to keep numerous different structural part configurations in store in order to quickly satisfy the constructional requirements of a motor bus of predetermined configuration.